Keying circuit for electronic musical instruments

ABSTRACT

A keying circuit for electronic musical instruments in whichbetween a bank of keyer circuits and a subsequent circuit such as a tone-coloring circuit, a tone-mixing circuit or a tone-signalamplifying circuit- there is provided a circuit including a resistor and a DC-bias-applying means. This arrangement may allow respective differences in DC potential between tone generators and said keyer circuits and between the latter and the subsequent circuit to be zero in direct coupling so that no DC isolation is needed which has hitherto been effected by employing capacitorresistor coupling circuits between circuit stages. This results in acquisition of an inexpensive keying circuit.

United States Patent Inventor Norio Tolnisawa Ilantamatsu, Japan Appl.No. 60,278 Filed Aug. 3, 1970 Patented Nov. 2, 1971 Assignee NipponGaltlti Seizo Kabusllikl Kaiaha llamalnatau-alti, Sltizuolta-lren, JapanPriorities Aug. 5, 1969 Aug. 5, 1969, Japan, No. 44/742360; Aug. 5,1969, Japan, No. 44/74361; Aug. 5, 1969, Japan, No. [7062; Nov. 20,1969, Japan, No. 44/110254 KEYING CIRCUIT FOR ELECTRONIC MUSICALINSTRUMENTS 6 Claims, 20 Drawing Figs.

US. Cl. 84/l.0l, 84/ 1.14

Int. Cl. G101: 1/00 Field of Search 84/1 .01,

[56] References Cited UNITED STATES PATENTS 2,599,510 6/1952 Campbell etal 84/].01 2,618,753 11/1952 Mierlo 307/115 2,959,693 11/1960 Meyer84/1.01

Primary Examiner-Milton O. l-lirshfield Assistant Exam iner-UlyssesWeldon Attorney-Cushman, Darby & Cushman ABSTRACT: A keying circuit forelectronic musical instruments in which--between a bank of keyercircuits and a subsequent circuit such as a tone-coloring circuit, atone-mixing circuit or a tone-signal-amplifying circuit-there isprovided a circuit including a resistor and a DC-bias-applying means.This arrangement may allow respective differences in DC potentialbetween tone generators and said keyer circuits and between the latterand the subsequent circuit to be zero in direct coupling so that no DCisolation is needed which has hitherto been effected by employingcapacitor-resistor coupling circuits between circuit stages. Thisresults in acquisition of an inexpensive keying circuit.

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An object of the present invention is to provide a keying circuit for anelectronic musical instrument permitting the omission of a number ofparts used in the circuit of this type so that it may be inexpensive.

Another object of the present invention is to provide an arrangement ofa keying circuit in which all stages of the circuit are directly coupledwithout using any capacitor-resistor coupling circuit.

A further object of the present invention is to provide an arrangementof a keying circuit to achieve no difference in potential between stagesof the circuit so as to make average DC voltages match the preceding aswell as the subsequent stages and also to prevent key click.

A still further object of the present invention is to provide anarrangement capable of compensating for tone outputs in a highaudiofrequency range.

Other object, features and advantages of the present invention willbecome apparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing anexample of a conventional keying circuit of this type;

FIG. 2 is a circuit diagram showing an embodiment of the presentinvention;

FIGS. 34 through 3f are views showing modifications of essentialportions of FIG. 1;

FIG. 4 is a circuit diagram showing another embodiment of the presentinvention;

FIG. 5 is a circuit diagram showing a further embodiment of the presentinvention;

FIGS. 6a through 60 are views showing modifications of essentialportions of FIG. 5;

FIG. 7 is a view showing a modification of the embodiment of FIG. 5;

FIG. 8 is a diagram showing an example of a circuit of this t e;

FIG. 9 is a diagram showing an improvement of the circuit shown in FIG.8 according to the present invention; and

FIGS. 10a and 10b are views showing modifications of essential portionsof FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Like references or symbolsindicate like parts hereunder.

Prior to describing the embodiments of the present invention,description of an example of the prior art will be made hereunder.

Referring to FIG. I, there is shown a conventional keying circuit, inwhich there are provided a number of tone generators A (shown. in block)each including a tone-generating oscillator, a frequency divider and(when necessary) an amplifier, which block A in the drawingschematically indicating only an output portion of the circuit. Anoutput terminal A, of each tone generator is connected through acapacitorresistor coupling circuit consisting of a DC blocking capacitorC, and a resistor R, with a mixing resistor R. The resistor R isconnected to one of two contacts of a corresponding keying switch S, andthe other contact is connected to a common connecting point a as a bankconnection point and then connected to an output terminal T of thekeying circuit. At the terminal 'I', a subsequent circuit B (shown in ablock) is connected through a coupling circuit consisting of a capacitorC anda resistor R and thus either a single tone signal or a synthesizedtone signal may be derived in accordance with the key operationassociated with the key switches S. That is, by the provision of thecapacitor C,., a DC voltage from the preceding stage such as the tonegenerator is blocked and by using the resistor R the DC potential at thecommon connecting point of the key switches is rendered zero. Such acoupling is known as a CR coupling which has been practiced in couplingbetween amplifiers. Therefore, if this coupling is used, there areneeded the CR coupling circuit as many as the number of the tonegenerators plus the subsequent circuits. This is disadvantageous in thatthe number of parts and the assembling cost become much greater, so thatthe circuit of this type has been very much expensive.

The present invention, therefore, has been worked out to obviate suchdrawbacks of the prior art as mentioned above.

Description of the present invention will be made on several embodimentsof the present invention by referring to the drawings.

Referring now to FIG. 2, there is shown a keying circuit arrangement ofan embodiment of the present invention as compared with the circuit ofFIG. I, in which reference A and A, indicate respectively tonegenerators and their output terminals which are the same as those inFIG. 1. Each of the output terminals is directly connected to a mixingresistor R and therefrom connected to a contact of the corresponding oneof a number of key switches S. The other contact is connected to acommon connecting point a and then connected to an output terminal T ofthe keying circuit through a voltagedropping resistor R,. At the point aand the terminal T, biasing power sources E, and E, are connectedthrough resistors R, and R, respectively.

By appropriately selecting the polarity and the amount of value ofvoltages of the sources E, and E, and so selecting the resistances ofthe resistors R. R, and R, the DC potential at the point a is set at thesame DC potential as that of the output terminal A, of the tonegenerator, while the DC potential at the output terminal T is renderedto be at the same level as the input DC potential of the subsequentcircuit 8 which may be one of a tone-coloring circuit, a mixing circuit,and an amplifier as known. Thus, a difference in DC potential betweenthe point a and the terminal T is burdened with a voltage drop acrossthe resistor R so that the tone generators and the subsequent circuitmay be used in a direct coupling therebetween, that is, without usingany coupling capacitor.

In operation, since the respective outputs of the tone generatorcircuits A are only different in frequency from one another, all of thecircuits A may be substantially of the same construction, and hence, theDC potentials at the output terminals A, may also be almost the same.Accordingly, if the DC potential at the other contact of the keyswitches is the same as those of the output terminals A, no potentialdifference occurs across the two contacts of the each key switch. Forthis reason, the construction, of FIG. 2 does not cause any key clickdue to the abovementioned DC potential difference upon playing thekey-operated electronic musical instrument.

Furthermore, the DC potential at the output terminal T is set to be thesame as that located at the input terminal of the subsequent circuit 8,and therefore, direct coupling does not adversely affect each terminal,so that the key switches and the subsequent circuit may perform theirnormal operations.

Of course, the means by which the DC potential at the common connectingpoint a of the key switches S is rendered to be the same levels as thoseat the output terminals A, of the tone generator circuits, and by whichthe DC potential at the output terminal T is rendered to be the same asthat on the subsequent circuit B side may be replaced, for example, bycircuits shown in FIGS. 3a through 3f, in which, one of the biasingpower sources is connected to a zero potential source. In other words,this means that said power source is grounded and that one power sourceis used in common to two biasing means, or in other words, for example,resistors are connected to form a bleeder resistor. Further, even whenthe subsequent circuit B is formed with an active element and even whenthe DC potential at the input side of circuit B is at zero, the

present circuit still can operate as desired by arranging the biasingpower source E so that it has an opposite polarity to that of the sourceE Referring to FIG. 4, there is shown another keying circuit arrangementembodying the present invention, in which a capacitor C for passing ACcomponents is connected in parallel with the resistor R in addition tothe circuit of FIG. 1. This capacitor serves to improve the transmissioncharacteristics of high-frequency signals, that is to say, it cancompensate for the drop of the levels in the tone signals due to theinfluence from the subsequent circuit.

Referring now to FIG. 5, there is shown a modified circuit of FIG. 2, inwhich the resistor R is provided with an intermediate tap to which oneend of the resistor R is connected, the other end thereof beinggrounded.

The tap may be used so that resistance portions of the resister Rdivided thereby at the point R serve as bleeder resistors fordetermining the respective DC potentials at the common connecting pointa and the output terminal T. This results is a reduction of the numberof the bleeder resistors used in the present circuit and greatlyfacilitates the settings of the above-mentioned DC potentials. FIGS. 60to 6e show various modification of biasing register network whichoperate in the same manner as those described in connection with FIGS.3a to 3f in regard to the circuit of FIG. 5.

FIG. 7 shows another arrangement which incorporates a capacitor C foreasily passing AC components of tone signals, in addition to thearrangement shown in FIG. 5. The capacitor may serve in the same manneras that described in connection with FIG. 4.

FIG. 9 shows a circuit of another embodiment of the present invention,which has been worked out as an improvement of the arrangement of FIG. 8which has been invented by the same inventor. More specifically, thekeying circuit of FIG. 8 has one thing which may be disadvantageous inthat it would be difficult to make a matching of the DC voltages betweenthe output terminals A of the tone generator circuits and an inputterminal a of an amplifier B since in the selection of the transistor 0,and in the designing of bleeder resistors Ra and Rb for biasing the baseof the transistor Q other significant requirements for the amplifierssuch as obtaining a desired amplification, selecting its input andoutput impedances so as to minimize the distortion thereof and enhancingthe working efficiency must simultaneously be satisfied.

In FIG. 9, at the common connecting point a is connected a potentialdifference compensating or adjusting circuit B including avoltage-dropping resistor R one end of which is connected through aresistor R to a power source +Vc c, and the other end being connected tothe subsequent amplifying circuit B at its input terminal A and aresistor grounded and connected to the base or terminal A of thetransistor 0,. The emitter of the transistor O is grounded through aresistor R and a capacitor C, connected in parallel to the resistor RThe collector of the transistor O is connected through a resistor R tothe power source +Vcc and also is connected to a signal output terminalA The potential at the terminal A can be set to provide a required basebias to the transistor 0,, and matched to the potential at the point aby making use of a voltage drop across the resistor R in DC directcoupling.

The same function as described above can be obtained by modifiedcircuits as shown in FIGS. 10a and 1012.

In FIG. 10a the transistor Q is arranged to constitute an emitterfollower circuit, whose base is grounded via a series circuit ofresistors R and R The connection point r between resistors R and R, isarranged to be connected to the common connecting point a. The base ofthe transistor Q. is connected through the resistor R to the powersource +Vcc.

FIG. 10b shows a modification of FIG. 9 by adding a bypass capacitor Cin parallel with the potential difference-adjusting resistor R Theeffects are the same as those previously described.

In the foregoing arrangements, the circuits as shown in FIGS. 9, 10a and10b are very much advanta eous in that the can thoroughly prevent keyclick due to thefiDC potential di ference between circuit connections aswell as are capable of desirably determining the bias voltage of anamplifying element such as a transistor in the amplifier by making useof the voltage difference-adjusting circuit.

I claim:

1. A keying circuit for an electronic musical instrument comprising:

a plurality of output terminals of tone generators, each terminal beingat a DC potential;

a plurality of keyer circuits, the input of each keyer circuit beingcoupled, relating to DC to the corresponding one of said outputtenninals;

a common connecting terminal to which all of the outputs of the keyercircuits are connected;

a resistor one end of which is connected to said common connectingterminal and the other connected to a subsequent circuit stage; and

DC biasing means substantially disposed at both ends of said resistor,whereby each of said tone generators may be directly coupled to thesubsequent circuit stage without using a coupling capacitor.

2. A keying circuit according to claim I, further comprising a capacitorconnected in parallel with said resistor.

3. A keying circuit according to claim 1, further comprising anintermediate tap provided in said resistor for permitting the resistorto be adapted as a bleeder resistance to adjust a difference betweenrespective potentials at the common connecting terminal and the input ofthe subsequent circuit stage.

4. A keying circuit according to claim 3, further comprising a capacitorconnected in parallel with said resistor.

5. A keying circuit according to claim 1, in which said subsequentcircuit is one of a tone-coloring circuit, a mixing circuit and anamplifier.

6. A keying circuit for an electronic musical instrument comprising apotential difference-adjusting circuit including a resistor and DCbiasing means substantially disposed at both ends of said resistor anddisposed between a bank of output terminals of keyer circuits and anamplifier circuit for amplifying the outputs of the keyer circuits,whereby a DC potential difference between output terminals of tonegenerators and an input terminal of the amplifier may be compensated forto achieve a direct DC coupling therebetween.

1. A keying circuit for an electronic musical instrument comprising: aplurality of output terminals of tone generators, each terminal being ata DC potential; a plurality of keyer circuits, the input of each keyercircuit being coupled, relating to DC to the corresponding one of saidoutput terminals; a common connecting terminal to which all of theoutputs of the keyer circuits are connected; a resistor one end of whichis connected to said common connecting terminal and the other connectedto a subsequent circuit stage; and DC biasing means substantiallydisposed at both ends of said resistor, whereby each of said tonegenerators may be directly coupled to the subsequent circuit stagewithout using a coupling capacitor.
 2. A keying circuit according toclaim 1, further comprising a capacitor connected in parallel with saidresistor.
 3. A keying circuit according to claim 1, further comprisingan intermediate tap provided in said resistor for permitting theresistor to be adapted as a bleeder resistance to adjust a differencebetween respective potentials at the common connecting terminal and theinput of the subsequent circuit stage.
 4. A keying circuit according toclaim 3, further comprising a capacitor connected in parallel with saidresistor.
 5. A keying circuit according to claim 1, in which saidsubsequent circuit is one of a tone-coloring circuit, a mixing circuitand an amplifier.
 6. A keying cIrcuit for an electronic musicalinstrument comprising a potential difference-adjusting circuit includinga resistor and DC biasing means substantially disposed at both ends ofsaid resistor and disposed between a bank of output terminals of keyercircuits and an amplifier circuit for amplifying the outputs of thekeyer circuits, whereby a DC potential difference between outputterminals of tone generators and an input terminal of the amplifier maybe compensated for to achieve a direct DC coupling therebetween.